1. Field of the Invention
The present invention relates to an air conditioning system with two compressors and a method for operating the same, and more particularly to an air conditioning system with two compressors and a method for operating the same, in which a value of a current required to operate the compressors does not exceed an allowable current range of a circuit breaker installed in a home when a first compressor is first operated and then a second compressor is sequentially operated, thereby safely controlling the air conditioning system and other household electric appliances using electric power.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating a flow of a refrigerant in a conventional air conditioning system, and FIG. 2 is a graph showing the variation of current value in the conventional air conditioning system. With reference to FIGS. 1 and 2, the conventional air conditioning system is described, as follows.
Generally, a conventional air conditioner achieves a cooling function via a cooling cycle formed by a refrigerant sequentially passing through a compressor, a condenser, an expansion valve, and an evaporator. Recently, air conditioners have used a four-way valve 20 for selecting the flow direction of the refrigerant installed in a conventional cooling apparatus, thereby reversing the function of each component so as to convert the cooling cycle into a heating cycle, in which an indoor heat exchanger 50 serves as a condenser and an outdoor heat exchanger 30 serves as an evaporator so as to discharge warm air into a room. Hereinafter, such an air conditioner is referred to as a heat-pump air conditioner.
Therefore, the heat-pump air conditioner achieves the cooling or heating cycle by selecting either of the cooling and heating modes, thereby being unlimitedly applicable in all seasons.
Hereinafter, the them “air conditioner” denotes the heat-pump air conditioner having cooling and heating functions, as well as the general air conditioner having a cooling function.
The conventional air conditioning system circulates a refrigerant via the cooling cycle shown in FIG. 1. With reference to FIG. 1, the conventional air conditioning system is described, as follows.
The conventional air conditioner comprises a plurality of compressors 10 for compressing a gaseous refrigerant in a low-temperature and low-pressure state so as to convert it into a high-temperature and high-pressure state. The compressors 10 includes first and second compressors 11 and 12 having different compression capacities of the refrigerant. The total compression capacity of the refrigerant in the air conditioning system is variably changed by simultaneously operating the first and second compressors 11 and 12 or selectively operating the first and second compressors 11 and 12, i.e. operating the first compressor 11 and stopping the second compressor 12.
Check valves 11a and 12a respectively prevent the reverse-flow of the refrigerant compressed by the first and second compressors 11 and 12.
A four-way valve 20 is further installed in the heat-pump air conditioner having the cooling and heating functions. The four-way valve 20 converts the flow direction of the refrigerant, thereby forming the cooling or heating cycle according to the converted flow direction of the refrigerant. Therefore, the general air conditioner only having the cooling function does not comprise the four-way valve 20. The four-way valve 20 supplies the refrigerant discharged from the compressors 10 to an outdoor heat exchanger 30 in a cooling mode, or to an indoor heat exchanger 50 in a heating mode, thereby alternating a circulation direction of the refrigerant.
The outdoor heat exchanger 30 serves as condensing means for condensing the gaseous refrigerant in the high-temperature and high-pressure state into a liquid refrigerant. An outdoor unit includes the outdoor heat exchanger 30, and an outdoor blower (not shown) installed next to the outdoor heat exchanger 30 so as to discharge air toward the outdoor heat exchanger 30 and increase heat exchange efficiency. The outdoor blower includes an outdoor fan (not shown) and a motor (not shown).
An expansion valve 40 expands the liquid refrigerant condensed by the condensing means into a two-phase refrigerant of liquid and gaseous phases in a low-temperature and low-pressure state.
The indoor heat exchanger 50 serves as evaporating means for converting the two-phase refrigerant into a gaseous refrigerant by absorbing external heat. An indoor unit includes the indoor heat exchanger 50, and an indoor blower (not shown), installed next to the indoor heat exchanger 50 so as to discharge cold air into the room. The indoor blower includes an indoor fan (not shown) and a motor (not shown).
An accumulator 60 separates the liquid phase from the two-phase refrigerant discharged from the indoor heat exchanger 50, and then supplies only the gaseous phase to the first and second compressors 11 and 12. Thereby, a cooling cycle consisting of compression, condensation, expansion, and evaporation is achieved.
In order to effectively achieve the cooling function of the above-described air conditioner, the compressors 10 include the first and second compressors 11 and 12 having different capacities. Herein, the first compressor 11 has a 60% compression capacity of the refrigerant, and the second compressor 12 has a 40% compression capacity of the refrigerant.
Therefore, when a cooling load is heavy, the first and second compressors 11 and 12 are simultaneously operated so that the total compression capacity of the refrigerant becomes 100%. When the cooling load is light, only the second compressor 12 is operated so that the compression capacity of the refrigerant totals only 40%. Thereby, the compression capacity of the refrigerant is variably changed.
As shown in FIG. 2, in order to rapidly satisfy the heavy cooling load, a current having an increased peak value (−Peak′ to +Peak′) for simultaneously operating the first and second compressors 11 and 12 is supplied to the first and second compressors 11 and 12 so that the total compression capacity of the refrigerant becomes 100% (P12). After that, a holding current for maintaining the simultaneous operation of the first and second compressors 11 and 12 is supplied to the first and second compressors 11 and 12 (M12).
However, in case the increased current peak value for simultaneously operating all of the compressors 10 exceeds an allowable current range of a circuit breaker installed in the home or building, which is provided with the air conditioning system, the circuit breaker cuts off power supplied to the home or building, thereby forcibly stopping the air conditioning system and all other electric appliances, thus causing their malfunction.
The circuit breaker employs a bimetal formed by attaching two metal plates having different expansion rates to each other. When an overcurrent exceeding the allowable current range flows within the circuit breaker, the circuit breaker, which is installed in the home or building, cuts off the power. That is, in case the total current supplied to the electric appliances connected to a power source exceeds the allowable current range of the circuit breaker, the circuit breaker cuts off the power, thereby forcibly stopping all of the electric appliances connected to the power source, and preventing any accidents generated by the overcurrent.
Particularly, in case where a plurality of appliances, such as the air conditioning system, requiring a comparatively increased current value at their early operation stage are installed in the home or building, it is more likely that the overcurrent will be cut off by the circuit breaker. Further, since the air conditioning system for rapidly satisfying the increased cooling load simultaneously operates all of the compressors whenever the cooling load is increased, the current value for operating the compressors more frequently exceeds the allowable current range of the circuit breaker. Therefore, it is difficult to safely control the above-described conventional air conditioning system.